The present invention relates generally to vibratory material screening apparatus employed in the classifying of solid particulate matter and, more particularly, to such screening apparatus which employs a rotatable tensioning assembly for tensioning of the screen in such apparatus.
Vibratory screening decks have been widely employed in the past for the classification and separation of particulate solids of varying particle sizes and compositions, such as limestone, coal and other ores. Such screening decks have typically comprised a generally rectangular frame which is suspended in operation and which has one or more screens in the frame upon which the materials to be classified are deposited. The frame and screening deck are suspended at an angle, and either the entire frame with the screen or the individual screens are vibrated to cause the solid particulates to move down the screen deck. As the materials move down the vibrating screen or screens, solids of smaller mesh size pass through the screen as "unders", and solids of larger dimensions are discharged from the lower end of the screen as "overs."
One form of such screening deck is disclosed in U.S. Letters Pat. No. 4,732,670. In the screening deck disclosed therein one or more wire cloth screens having a predetermined mesh size to permit the passage therethrough of material are anchored at opposite ends of the screens to members extending transverse to the frame walls. In such screening deck one end of the screen is stationarily anchored over its width, and the other end of the screen is anchored to a rotatable tensioning assembly which, when rotated, adjusts the tension across the width of the screen.
Although the aforementioned rotatable tensioning assembly produces a screen tension across its width which is sufficently uniform to be satisfactory in many installations and uses, the degree of uniformity of the tension may not be entirely satisfactory in some installations, depending upon the width of the screening deck, the screen wire diameter and spacing and the needs of the user. This is because some degree of differential in tension across the width dimension of the screen in these latter installations may arise due to a differential in torque which may occur over the length of the rotatable tensioning tube when a tension is taken on the screen by the rotatable tensioning assembly. For example, where the rotatable tube of the rotatable tensioning assembly is rotated at each of its ends, the anchoring element on the surface of the tube may rotate over a greater distance adjacent its ends where the torque is applied to the tube than in the center of the tube because of the tensile characteristics of the elongate rotatable tube. As a result of this torque difference, a greater tension will tend to result in the screen at its outer edges than in the center. Due to this difference in screen tension across the width dimension of the screen, either one of two undesirable conditions may result.
One condition that might arise is that if the center of the screen is properly tensioned, the edges of the screen may be over-tensioned. Although the over-tensioning of the screen edges will actually improve the "whip" of the screen and have a beneficial result on production, such over-tensioning will result in fatigue in the screen wire adjacent its edges and unacceptable early wear of the screen adjacent its edges requiring early screen replacement.
The other condition that might arise is that if the edges of the screen are properly tensioned, the center of the screen may be under-tensioned. This does reduce the rate of wear of the screen, but results in decreased and inefficient production adjacent the center of the screen.
The improved tensioning assembly of the present invention overcomes the aforementioned shortcomings. In the improved tensioning assembly incorporating the principles of the present invention, the uniformity of screen tension adjustment in a rotatable tensioning assembly may be easily and accurately accomplished across the entire width dimension of the screen. Thus, excessive wear is substantially reduced and screen efficiency and production substantially improved.
In one principal aspect of the present invention, a classifying apparatus comprises a rigid frame and a classifying screen in the frame. Anchor means anchors one end of the screen, and first tensioning means for tensioning the screen includes at least one elongate rotatable means adjacent the other end of the screen which extends substantially across the width of the other end of the screen. The improvement in the apparatus comprises second tensioning means for selectively and incrementally adjusting the tension on the screen along the dimension over which the rotatable means extends.
In another principal aspect of the present invention, the second aforementioned tensioning means comprise the anchor means.
In still another principal aspect of the present invention, the second tensioning means comprise an elongate rigid beam which extends across the frame adjacent the one end of the screen, and the anchor means includes at least one screen anchor which also extends across the frame in spaced relationship to the beam. An adjustment means is provided for selectively and incrementally adjusting the space between the beam and the anchor along their respective lengths.
In still another principal aspect of the present invention, the aforementioned adjustment means adjusts the space by flexing the anchor along its length relative to the beam.
In still another principal aspect of the present invention, the aforementioned adjustment means flex the anchor by a greater amount adjacent its center than adjacent its ends.
In still another principal aspect of the present invention, the aforementioned adjustment means threadedly adjusts the space.
In still another principal aspect of the present invention, a method of adjusting the tension of the screen of a classifying apparatus includes the steps of attaching one end of the screen to an anchor means, attaching the other end of the screen to a rotatable tensioning means, rotating the rotatable tensioning means to exert a tension on the screen across a dimension of the screen, and adjusting the anchor means to selectively and incrementally further adjust the tension of the screen across the aforementioned dimension of the screen.
In still another principal aspect of the present invention, the anchor means is flexed in the aforementioned method to selectively and incrementally further adjust the tension of the screen.
In still another principal aspect of the present invention, the anchor means is flexed in the aforementioned methods by a greater degree adjacent the center of the screen than adjacent the edges.
In still another principal aspect of the present invention, the anchor means is threadedly flexed in the aforementioned methods.
In still another principal aspect of the present invention, an anchor assembly for the screen of a classifying apparatus includes an elongate rigid beam and anchor means for anchoring the screen. The anchor means extends in spaced substantially parallel relationship to the beam and includes mounting means for mounting one end of the screen thereto. Adjustment means extends between the beam and the anchor means for selectively flexing the anchor means to adjust the size of the space between the anchor means and the rigid beam over the length of the beam.
In still another principal aspect of the present invention, in the aformentioned assembly the beam and the anchor means are substantially coextensive in length and their ends are fixed against movement relative to each other.
In still another principal aspect of the present invention, the adjustment means in the aforementioned anchor assemblies include threaded means extending between the beam and the anchor means intermediate their ends.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.